In an industrial plant, for example in a power generation plant, individual plant components are connected to one another by a control system (process control system), in particular a digital control system. Such a plant component may be a valve or a motor for example. An individual plant component usually interacts here with a multiplicity of other plant components, and its operating state is dependent on the operating states of the other plant components. The control system is used to monitor the operating states, and the plant is controlled automatically or manually. To operate the plant, it is necessary to record the data of the various plant components and establish the interrelationships between the data. Based on this data, a control instruction is then sent by the process control system to the respective plant component, either automatically or in response to a manual input instruction of the operator.
For the control of a plant component, a so-called control or function module is usually employed in the control system to record the individual data, evaluate it and if appropriate, forward it after preprocessing.
Owing to the manifold ways in which the plant components interact and the resulting large volume of data, the control or function modules are very large and complex. The greater their complexity, the more difficult it becomes to follow the internal function sequences of the individual control module. Owing to the manifold interactions to be taken into account, the creation of a control module is likewise highly complex, and consequently time-consuming. Moreover there is a risk of errors arising during the design and programming of the control module which are not detected.
Adapting an existing control module to a specific plant also requires a multiplicity of settings and parameter inputs. Only then can the existing control module be integrated in the process control system of the specific plant. Users find it difficult to grasp the complex dependencies within the control module and its functions. As a result, modifying an existing control module is time-consuming and requires a lot of effort. In addition, it is very difficult to predict the effects of modifications to the control module, that is to say to specific circuits or program flows. Moreover, the control module is often not used optimally, so that some of its functions remain unused. For the most part, control modules are intentionally equipped with a large number of functions to cover as many requirements as possible. This requires a large amount of computing power, even if the multiplicity of functions is not necessary for a specific plant.
Described in WO97/03389 is a method for creating a function plan in which inputs and outputs of modules displayed on the screen are connected to one another by a user drawing lines. A program stored in the computer then performs a plausibility check on the connections between the modules.
The disadvantage of this is that drawing lines is prone to errors and the subsequent plausibility check is costly.